Computer-aided detection (CAD) generally refers to the use of computers to analyze medical images to detect anatomical abnormalities therein. Sometimes used interchangeably with the term computer-aided detection are the terms computer-aided diagnosis, computer-assisted diagnosis, or computer-assisted detection. CAD results are mainly used by radiologists and other medical professionals as “secondary reads” or secondary diagnoses tools. When analyzing a medical image, the radiologist usually makes his or her own analytical determinations before looking at the CAD results, which either verify those determinations or trigger further inspection of the image. Some CAD implementations have used CAD results in a “concurrent reading” context in which the radiologists look at the CAD results at the same time that they look at the images.
In the field of mammography, thousands of mammography CAD systems are now installed worldwide, and are used to assist radiologists in the interpretation of millions of mammograms per year. Mammography CAD systems are described, for example, in U.S. Pat. No. 5,729,620, U.S. Pat. No. 5,815,591, and U.S. Pat. No. 5,917,929, each of which is incorporated by reference herein. Mammography CAD algorithms analyze digital or digitized images of standard mammographic views (e.g. CC, MLO) for characteristics commonly associated with breast cancer, such as calcifications, masses, and architectural distortions. The outputs of CAD systems, generally referred to herein as CAD results, are sets of information sufficient to communicate the locations of anatomical abnormalities, or lesions, in a medical image, and can also include other information such as the type of lesion, degree of suspiciousness, and the like. CAD results are most often communicated in the form of reduced-resolution versions of the different mammographic views containing annotations that identify the location and type of potential abnormality. The radiologist analyzes the original mammogram, either in film format on a light box or in digital form on a softcopy workstation, and then reviews the CAD results, usually on a display monitor or a paper printout.
Workflow processes associated with mammography, including CAD-related workflow processes, implicate substantial cost issues in practical clinical environments. “All-digital” mammography environments, in which digitally captured mammograms could be automatically shepherded, with little or no human intervention, through CAD systems and related HIS/RIS (Hospital Information System/Radiology Information System) equipment directly to the radiologists' viewing workstations, have not yet become common. According to one estimate, approximately 90 percent of all mammography systems worldwide are still film-based units, and an equivalent percentage of all mammograms taken yearly are film-based mammograms rather than digital mammograms. Because film-based mammograms require digitization prior to performance of CAD algorithms, a substantial number of workflow-related issues can arise.
One important issue relates to the scanning and identification process for film-based mammograms. For a CAD algorithm to be effective, it is usually desirable for a typical 18×24 cm or 24×30 cm film mammogram to be digitized at about 50 microns of spatial resolution and about 12 bits of dynamic range. Even using today's scanning technologies, it can take a commercial film scanner 15-60 seconds to digitize one film at these resolutions, and therefore it can take 1-4 minutes to digitize a typical film case having 4 views. A stack of 20 cases can therefore take an hour to run through the digitizer. At least theoretically, the technologist who placed the film stack in the scanner should be able to perform other duties while the digitization is taking place. Progress has been made toward automation of the film scanning process. One example is WO 02/45437 A2, which is incorporated by reference herein, which describes automatic film orientation and identification based on lead view marker and breast outline segmentation. Another example is Published US Patent Application No. US20060126909A1, Ser. No. 10/998,121, filed on Nov. 26, 2004, which describes a graphical status indicator having a plurality of spatially ordered film case icons that graphically communicate a current state of the scanning to a technologist who may be performing other duties while the digitization is taking place. However, practical problems may still arise which may cause the technologist to spend substantial time and attention in the scanning and image identification process.
In order for the scanned images to be correctly identified and properly stored, each image must have information correctly associated with it. This information includes the case to which it belongs, as well as type of image (which side and which view). Film-based medical image scanning systems have conventionally assumed that each case to be scanned has a certain number of films and the films are stacked in a particular order. This predefined standard scanning protocol is defined by the manufacturer in advance based on what the manufacturer expects its most likely application to be. In many cases this standard scanning protocol is chosen as the common mammography screening case in the United States. This is commonly comprised of four films per study, ordered as follows: R MLO, L MLO, R CC and L CC.
However, a problem with such conventional approaches arises when the scanning system receives a case that does not have the same number of films, the films are ordered differently, and/or the views do not correspond to the standard scanning protocol set by the manufacturer. Even when automatic film orientation and identification is available, the lead markers may be inadequate. For example, the lead marker may be partially out of the frame or may be overlapping with part of the breast tissue or patient label. Further, the lead marker detection systems may especially have trouble correctly identifying view types that are not one of the four standard screening views.
Errors in film identification are costly and time consuming to correct. If the error is noticed by the technologist during the scanning process, the technologist may use a user interface to manually identify each image. If the technologist does not notice the error, the film may be associated with the wrong case. The radiologist may recognize the error during his or her review, and expend valuable time making a correction.
If the technologist or technician responsible for scanning the cases knows ahead of time that the case does not conform to the standard scanning protocol, the information may be manually entered. However, this may be unduly time consuming, and in many cases such non-standard cases are simply not scanned. If the case is not scanned at all, not only does the case forego the potential benefits of CAD processing, the case is also unavailable for analysis and comparison in later years, at a time when the move to all digital mammography may have taken place at the particular medical facility.
It is important to note that there are many ways in which the case may not conform to the manufacturer's standard scanning protocol. For example, diagnostic mammography cases commonly have more than four films and include other types of views such as ML, LMO, LM, XCC, XCCL, XCCM, FB and SIO for each breast. Certain types of populations may have different imaging procedures. For example, in some medical imaging facilities, certain ethnic populations may have a different standard screenings. A patient my have only one breast due to a prior mastectomy. Some geographic regions may have different screening protocols. For example in the Netherlands, after a standard four-film screening, in subsequent years screening mammography cases typically consist only of two films: R MLO and L MLO.
Some systems allow the user to specify a different number of films per case. One example is the SecondLook® 700 system from iCAD, Inc., which allows users to specify the number of slides per study. However, if one case in a large stack of cases has a missing film, or and extra film, then all of later scanned cases in the stack can have costly identification errors. Moreover, the user still must go through a time consuming process for each film of each case to identify the laterality, view and other critical information if the cases do not match one the standard cases supplied by the manufacturer.
Accordingly, it would be desirable to provide a system for medical film digitization that is easier for a technologist cases that do not correspond to a standard case that has been defined by the manufacturer, thereby leading to cost savings and increased productivity.
It would be further desirable to provide such a digitization and/or processing system in a manner that flexibly accommodates cases of different composition, thereby increasing the likelihood that the case is digitized and stored, thereby facilitating evolution from film environments to digital environments.